1. Field of the Invention
The invention relates to a drive system for a motor vehicle and to a motor vehicle having such a drive system. The invention can be applied to any motor vehicles, but the invention and the problems on which it is based are explained in more detail with respect to a passenger motor vehicle.
2. Description of the Related Art
A hybrid vehicle generally denotes a vehicle with a drive system that has plural drive units, for example an internal combustion engine and an electric machine. Parallel hybrid drives permit the electric machine and the internal combustion engine to apply a torque to a transmission either alternatively or cumulatively and are used to generate an energetic efficiency level that is as high as possible. The electric machine also can be used as a generator, i.e. during the braking of the vehicle. Thus, the braking energy of the vehicle, which is present in the form of kinetic energy, can be recovered and used, for example, to charge electric energy stores. Frequent starting processes and acceleration processes that occur, for example, in urban traffic, preferably are carried out or assisted by the electric machine in a hybrid motor vehicle since the operation of the internal combustion engine with frequent load changes results in increased fuel consumption and emissions of pollutants.
The electric machine also is assigned the task of starting the internal combustion engine. In this context, both reliable warm starting, for example restarting after the internal combustion engine has been switched off for a brief time, and reliable cold starting of the internal combustion engine must be ensured.
JP 2003328907 A describes a drive system for a hybrid vehicle having an internal combustion engine, a belt starter generator connected to the crankshaft of the internal combustion engine and a pinion starter that can be connected to a starter ring gear of the internal combustion engine. The belt starter generator reliably permits the internal combustion engine to start from the warm state, and the belt drive allows a generator mode of the belt starter generator over a wide range of rotational speeds of the internal combustion engine. The pinion starter can provide a significantly larger torque than the belt starter generator and reliably ensures cold starting of the internal combustion engine. However, the direct connection of the belt starter generator to the internal combustion engine disadvantageously makes it possible to drive the vehicle axles solely with the belt starter generator only if the internal combustion engine is entrained. Thus, friction losses increase. Decoupling the internal combustion engine also is impossible during the conversion of kinetic energy of the hybrid vehicle into electric energy by means of the belt starter generator. As a result, the internal combustion engine also generates drag torques and friction losses during the conversion of braking energy.
The invention therefore is based on the object of providing an improved drive system that eliminates the abovementioned disadvantages.